EUV light source and exposure apparatus

ABSTRACT

An extreme ultraviolet (EUV) light source is provided. The EUV light source comprises a spray nozzle array having a plurality of spray nozzles configured to spray a plurality of rows of droplets to an irradiating position; a laser source configured to generate a first laser beam and a second laser beam and cause the first laser beam and the second laser beam to alternately bombard the rows of droplets to generate EUV light with increased output power; a focusing mirror having at least two first sub-focusing mirrors and at least two second sub-focusing mirrors; and a first driving device having at least two first sub-driving device and at least two second sub-driving device, each of first driving devices driving one of the first sub-focusing mirrors and each of the second sub-driving devices driving one of the second sub-focusing mirrors.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the priority of Chinese patent application No. 201410549374.9, filed on Oct. 16, 2014, the entirety of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention generally relates to the field of semiconductor manufacturing technology and, more particularly, relates to EUV (extreme ultraviolet) light sources, methods for generating EUV light, and exposure apparatus.

BACKGROUND

Photolithography is one of the important steps in the semiconductor manufacturing technology, which utilizes an exposure process and a developing process to form patterns in a photoresist layer. With the continuous increase of the integration level of IC chips, the critical dimension of features to be formed by a photolithography process has become smaller and smaller.

The minimum critical dimension of the features formed by a photolithography process may be determined by the resolution (R) of an exposure apparatus. The resolution of the exposure apparatus is described by an equation: R=Kλ/(NA), wherein “K” refers to a coefficient related to an exposure process; “λ” refers to the wavelength of the exposure light; and “NA” refers to the numerical aperture of the optical system of the exposure apparatus. According to such an equation, there may be two approaches to increase the resolution of the exposure apparatus: increasing the numerical aperture of the optical system; and reducing the wavelength of the exposure light.

A lot of efforts have been made on increasing the numerical aperture of the optical system of the exposure apparatus. However, because the next generation photolithography technique has strict requirement for the minimum critical dimension, it often requires the optical system to have a large numerical aperture. Thus, it may cause the manufacturing and modulating of the optical system to be complex, and further increasing the numerical aperture may have a significant limitation on the focus depth of the optical system.

Therefore, the other approach, reducing the wavelength of the exposure light, has been deployed to increase the resolution of the exposure system. Extreme ultraviolet (EUV) source is a recently developed light source. The wavelength of the EUV light is approximately 13.5 nm, or shorter. When the EUV light source is used in an exposure system, the critical dimension of the formed features may be substantially small. The mainstream method for generating EUV light is to use Laser Produced Plasma (LPP). The principle of LPP is to bombard a target made of Sn to generate plasma; and the plasma radiates ultraviolet light.

FIG. 1 illustrates an existing EUV light source. As shown in FIG. 1, the EUV light source includes a Sn spray nozzle 101. The Sn spray nozzle 101 sprays Sn droplets 102 downwardly. The EUV light source also includes a laser source 103. The laser source 103 generates a laser beam 104. The laser beam 104 is focused by the lens unit 105; and is used to bombard the Sn droplets 102. The bombarded Sn droplets 102 generates plasma; and the plasma radiates EUV light 108. Further, the EUV light source also includes a single-piece focusing mirror 107. The focusing mirror 107 collects the radiated EUV light 108; and further focuses the collected EUV light 108 at a central focusing point 109.

However, the power of the EUV light generated by such EUV light source is relative low, and it may be unable to match the manufacturing requirements. The disclosed EUV light source and exposure apparatus and other aspects of the present disclosure are directed to solve one or more problems set forth above and other problems.

BRIEF SUMMARY OF THE DISCLOSURE

One aspect of the present disclosure includes an extreme ultraviolet (EUV) light source. The EUV light source comprises a spray nozzle array having a plurality of spray nozzles configured to spray a plurality of rows of droplets to an irradiating position; a laser source configured to generate a first laser beam and a second laser beam and cause the first laser beam and the second laser beam to alternately bombard the rows of droplets to generate EUV light with increased output power; a focusing mirror having at least two first sub-focusing mirrors and at least two second sub-focusing mirrors; and a first driving device having at least two first sub-driving device and at least two second sub-driving device, each of first driving devices driving one of the first sub-focusing mirrors and each of the second sub-driving devices driving one of the second sub-focusing mirrors.

Another aspect of the present disclosure includes a method for generating EUV light. The method includes spraying a plurality of droplets downwardly to an irradiating position through a spray nozzle array having a plurality of spray nozzles; performing a scanning using a laser source to sequentially bombard the droplets arriving at the irradiating position to generate EUV light from each of the plurality of droplets; and collecting and focusing the EUV light at a central focusing point by a focusing mirror having at least two first sub-focusing mirrors and at least two second sub-focusing mirrors; and a first driving device having at least two first sub-driving device and at least second sub-driving device.

Another aspect of the present disclosure includes an exposure apparatus. The exposure apparatus includes a base; an EUV light source with an enhanced power configured as a light source for a photolithography process; a wafer stage configured to hold a wafer for forming patterns by the photolithography process; a reticle stage configured to hold a reticle for the photolithography process; and a control unit configured to control the exposure apparatus to perform the photolithography process. Wherein the EUV light source comprises a spray nozzle array having a plurality of spray nozzles, a focusing mirror having at least two first sub-focusing mirrors and at least two second sub-focusing mirrors, and a first driving device having at least two first sorb-driving devices and at least second sub-driving device.

Other aspects of the present disclosure can be understood by those skilled in the art in light of the description, the claims, and the drawings of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an existing EUV light source;

FIG. 2 illustrates an exemplary EUV light source according to the disclosed embodiments;

FIG. 3 illustrates another exemplary EUV light source according to the disclosed embodiments;

FIGS. 4-5 illustrate certain detailed structures of the EUV light source illustrated in FIG. 3;

FIG. 6 illustrates control signals of an exemplary EUV light source according to the disclosed embodiments;

FIGS. 7-8 illustrate structures corresponding certain stages of an exemplary method for generating EUV light according to the disclosed embodiments;

FIG. 9 illustrates a block diagram of an exemplary exposure apparatus according to the disclosed embodiments; and

FIG. 10 illustrates an exemplary method for generating EUV light according to disclosed embodiments.

DETAILED DESCRIPTION

Reference will now be made in detail to exemplary embodiments of the invention, which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

The power of the EUV light generated by the EUV light source illustrated in FIG. 1 is relatively low. For example, the power may be in a range of approximately 10 W˜30 W. In a practical photolithography process, the required power may be up to approximately 250 W. Thus, the EUV light generated by the EUV light source illustrated in FIG. 1 may be unable to match the practical requirements.

Referring to FIG. 1, the Sn droplets 102 sprayed from the Sn spray nozzle 101 are mechanically controlled such that the adjacent Sn droplets 102 are spatially separated. By doing so, the focused laser beam 104 may be able to bombard each of the Sn droplets 102. When each of the Sn droplets 102 is bombarded, plasma may be generated; and the plasma may irradiate EUV light. If the distance between two adjacent Sn droplets 102 is substantially small, and/or two Sn droplets 102 stick together, when the focused laser beam 104 bombards the problematic Sn droplets 102, a fragment plasma may be generated; and the fragment plasma may affect the following Sn droplets 102. Thus, the bombardment effect of the focused laser beam 104 may be impaired; and/or it may be difficult to collect and focus the irradiated EUV light. Therefore, the power of the EUV light source may be adversely affected.

To ensure the completeness of each drop of the Sn droplets 102; and to cause adjacent Sn droplets 102 to have a desired distance, the spray frequency of the mechanically controlled spray nozzle 101 may be approximately 100 kHz. Thus, the number of the Sn droplets 102 sprayed per unit time may be limited. In another word, the number of the Sn droplets 102 bombarded by the focused laser beam 104 may be limited. Thus, the quantity of the plasma generated by the bombarded Sn droplets 102 and the quantity of the EUV light irradiated by the plasma may be limited. Ultimately, the quantity of the EUV light focused at the central focusing point 109 may be limited. Thus, the power of the EUV light focused at the central focusing point 109 may be relatively low.

FIG. 2 illustrates an exemplary EUV light source according to the disclosed embodiments. As shown in FIG. 2, the EUV light source may include a spray nozzle array 201. The spray nozzle array 201 may include a plurality of spray nozzles 21 distributed along a scanning direction 200. The plurality of spray nozzles 21 may be configured to spray a plurality of droplets 22 downwardly to an irradiating position 202. The plurality of droplets 22 may form a plurality of rows. The scanning direction 200 may refer to a direction parallel to x-axis. The irradiating position 202 may referred to a position at which a laser beam may bombard the plurality of droplets 22 to irradiate EUV light.

Further, the EUV light source may also include a laser source 203. The laser source 203 may be configured to generate a first laser beam 31 and a second laser beam 32; and may cause the first laser beam 31 and the second laser beam 32 to scan along the scanning direction 200. The first laser beam 31 and the second laser beam 32 may alternately bombard the plurality of droplets 22 at the irradiating position 202 during the scanning process. The plurality of droplets 22 may generate plasma when being bombarded by the first laser beam 31 and the second laser beam 32; and the plasma may irradiate EUV light.

The laser source 203 may include a laser 204, a reflective mirror 209 and a first driving device (not labeled) including a first sub-driving device 205 and a second sub-driving device 206. The laser 204 may be configured to generate a laser beam. The reflective mirror 209 may be configured to reflect the laser beam to cause the laser beam to irradiate the irradiating position 202. The first driving device may be connected with the reflective mirror 209 to drive the reflective mirror 209 to rotate. When the reflective mirror 209 is rotating, the laser beam reflected by the reflective mirror 209 may scan along the scanning direction 200 to sequentially bombard the droplets 22 at the irradiating position 202.

Specifically, the reflective mirror 209 may include a first reflective mirror 207 and a second reflective mirror 208; and the first driving device may include the first sub-driving device 205 and the second driving device 206. The first reflective mirror 207 may be disposed above the second reflective mirror 208. The first reflective mirror 207 may reflect a portion of the laser beam generated from the laser 204 to form the first laser beam 31. Further, the first sub-driving device 205 may be connected with the first reflective mirror 207 to drive the first reflective mirror 207 to rotate. When the first reflective mirror 207 is rotating, the first laser beam 31 may scan along the scanning direction 200 to sequentially bombard the droplets 22 at the irradiating position 202.

The second reflective mirror 208 may reflect a portion of the laser beam generated by the laser 204 to form the second laser beam 32. The second sub-driving device 206 may be connected with the second reflective mirror 208 to drive the second reflective mirror 208 to rotate. When the second reflective mirror 208 is rotating, the second laser beam 32 may scan along the scanning direction 200 to sequentially bombard the droplets 22 at the irradiating position 202.

Therefore, as shown in FIG. 2, the spray nozzle array 201 may include a plurality of spray nozzles 21. The plurality of spray nozzles 21 may sequentially spray the plurality of droplets 22 downwardly to the irradiating position 202. Thus, the supplying quantity of the droplets 22 per unit time may be increased. Further, different spray nozzles 21 sequentially spray the plurality of droplets 22, which may ensure adjacent droplets 22 to have a certain distance. Further, the laser beam, including the first laser beam 31 and the second laser beam 32, may scan along the scanning direction 200; and sequentially bombard the droplets 22 at the irradiating position 202 to irradiate EUV light.

Thus, every droplet 22 at the irradiating position 202 may be bombarded by the laser beam; and the quantity of the irradiated EUV light may be increased. Further, the light focusing device 215 may perform a rotating scanning to collect the EUV light irradiated from the plasma generated by different droplets 22; and to focus the collected EUV light at the central focusing point 220. Thus, the power of the EUV light outputted from the central focusing point 200 may be increased.

FIG. 3 illustrates another exemplary EUV apparatus according to the disclosed embodiments. As shown in FIG. 3, the EUV light source may include a spray nozzle array 201. The spray nozzle array 201 may include a plurality of spray nozzles 21 distributed along a scanning direction 200. The plurality of spray nozzles 21 may be configured to spray a plurality of droplets 22 downwardly to an irradiating position 202. The scanning direction 200 may refer to a direction parallel to the x-axis. The irradiating position 202 may refer to a position at which a laser beam may bombard the droplets 22 to irradiate EUV light.

Further, the EUV light source may also include a laser source 203. The light source 203 may be configured to generate a first laser beam 31 and a second laser beam 32; and cause the first laser beam 31 and the second laser beam 32 to scan the scanning direction 200. During the scanning process, the first laser beam 31 and the second laser beam 32 may sequentially bombard the droplets 22 in different rows of droplets 22 at the irradiating position 202. The droplets 22 may generate plasma when being bombarded by the first laser beam 31 or the second laser beam 32; and the plasma may irradiate EUV light.

Further, the EUV light source may also include a light focusing device 215. The light focusing device 215 may have an elliptical surface; and the elliptical surface may face the irradiating position 202. Further, the light focusing device 215 may include a light focusing mirror (not labeled) and a first driving device connected with the light focusing mirror. The first driving device may drive the light focusing mirror to perform rotating scanning to collect the EUV light irradiated from the droplets 202; and focus the collected EUV light at the central focusing point 220.

The light focusing mirror may include a top focusing mirror 212 and a bottom focusing mirror 213. The top focusing mirror 212 and the bottom focusing mirror 213 may be separated; and the top focusing mirror 212 may be disposed over the bottom focusing mirror 213.

Further, the top focusing mirror 212 may include at least two first sub-light focusing mirrors 212 a; and the bottom focusing mirror 213 may include at least two second sub-light focusing mirrors 213 a. Two first sub-light focusing mirrors 212 a and two second sub-light focusing mirrors 213 a are shown in FIG. 3 for illustrative purposes. The first driving device may include at least two first sub-driving device 216 a and at least two second sub-driving device 217 a. Each of the first sub-driving device 216 a may be connected with one of the first sub-focusing mirrors 212 a; and each of the second sub-driving device 217 a may be connected with one of the second sub-focusing mirrors 213 a. The two first sub-driving device 216 a may drive the corresponding two first sub-focusing mirrors 212 a to perform a rotating scanning; and the two second sub-driving device 217 a may drive the corresponding two second sub-focusing mirrors 213 a to perform a rotating scanning.

Further, the EUV light source may also include a droplet material supply chamber (not shown). The droplet material supply chamber may be configured to store the material of the droplets 22. The plurality of spray nozzles 21 of the spray nozzle array 201 may be connected with the droplet material supply chamber by certain interconnect tubes (not shown); and the material stored in the droplet material supply chamber may be sprayed out from the spray nozzles 21 to form the droplets 22. In certain other embodiments, the droplet material supply chamber may be more than one; and each of the plurality of spray nozzles 21 may be connected with a corresponding droplet material supply chamber by a certain interconnect tube.

The spray nozzle array 201 may also include a plurality of switches (not shown) corresponding to the plurality of spray nozzles 21. Each of the plurality of switches may control a corresponding spray nozzle 21 to spray, or not to spray droplets 22. The switches may be disposed in the interconnect tube between the spray nozzles 21 and the droplet material supply chamber. By controlling on/off of the switches, the material stored in the droplet material supply chamber may be feed to the spray nozzles 21 with pre-determined intervals through the interconnect tube. Thus, the droplets 22 may be sprayed to the irradiating position 202.

The switches may be signal-controlled mechanical switches. That is, the on/off status of the switches may be controlled by electrical signals; and the spray nozzles 21 may be controlled to spray or not to spray droplets 22 downwardly. In one embodiment, the switches are electronic extruding switches.

The droplets 22 may be made of any appropriate material, such as Sn, Sn alloy, Sn compounds, Xe, or Li, etc. The Sn compounds may include SnBr₄, SnBr₂, and SnH₄, etc. The Sn alloy may include SnGa alloy, SnIn alloy, or SnInGa alloy, etc.

The material of the droplets 22 may determine the temperature of the droplets 22 at the irradiating position 202. The distance between the plurality of spray nozzles 21 and the irradiating position 202 may be designed according to practical requirements. The number of the spray nozzles 21 may be greater than two.

Referring to FIG. 3, in one embodiment, the scanning direction 200 may be the direction parallel to the x-axis direction. The irradiating position 202 may be a line (refer to the dashed line) just below the spray nozzle array 201 and parallel to the scanning direction 200. Further, the irradiating position 202 may be corresponding to a first focus point of the elliptical surface of the focusing mirror; and the central focus point 220 may be corresponding to the second focus point of the elliptical surface of the light focusing mirror. When the first focus point is moving along a linear direction parallel to the scanning direction 200, the focusing mirror may perform a rotating scanning to keep the position of the second focus point to be relatively constant. In certain other embodiments, the light focusing mirror may scan with other appropriate mode.

FIG. 4 illustrates the detailed structure of the spray nozzle array 201 according to the disclosed embodiments. As shown in FIG. 4, the spray nozzle array 201 may include a plurality of spray nozzles 21 distributed along the scanning direction 200. The plurality of spray nozzles 21 may be sequentially referred as a first spray nozzle 21 a ₁, a second spray nozzle 21 a ₂, a third spray nozzle 21 a ₃, . . . , and an Nth spray nozzle 21 a _(n), along the scanning direction 200. Being distributed along the scanning direction 200 may refer that a connection line of the centers of the plurality of spray nozzles 21 (21 a ₁˜21 a _(n)) is parallel to the scanning direction 200.

In one embodiment, the distances (Ds) between the centers of adjacent spray nozzles 21 may be a constant. In certain other embodiments, the distances (Ds) between the center of adjacent spray nozzles 21 may be different.

The plurality of spray nozzles 21 (21 a ₁˜21 a _(n)) may be able to sequentially spray droplets 22 to the irradiating position 202 to cause the lateral distances (W) between adjacent droplets 22 to be equal to a constant (W=D). Thus, when the laser beams (the first laser beam 31 and the second laser beam 32) are scanning along the scanning direction 200, the laser beams may sequentially bombard each of the plurality of droplets 22 at the irradiating position 202. Such a configuration may ensure that a following droplet 22 may not be affected by the fragment plasma generated by bombarding the current droplet 22.

In one embodiment, the distance between the centers of adjacent spray nozzles 21 may be in a range of approximately 45 μm˜75 μm. The size of the droplets 22 may be in a range of approximately 25 μm˜35 μm. In one embodiment, the droplets sprayed from the first spray nozzle 21 a ₁ may be referred as first droplets; the droplets sprayed from the second spray nozzle 21 a ₂ may be referred as second droplets; the droplets sprayed from the second spray nozzle 21 a ₃ may be referred as third droplets, . . . ; and the droplets sprayed from the Nth spray nozzle 21 a _(n) may be referred as Nth droplets.

A process for the plurality of spray nozzles 21 (21 a ₁˜21 a _(n)) sequentially spraying droplets 22 to the irradiation position 202 may include: spraying a first droplet not labeled) through the first spray nozzle 21 a ₁; spraying a second droplet (not labeled) through the second spray nozzle 21 a, after the first droplet is sprayed for a pre-determined first time duration; spraying a third droplet (not labeled) through the third spray nozzle 21 a ₃ after the second droplet was spray with for a predetermined second time duration; . . . ; and spraying an Nth droplet (not labeled) through the Nth spray nozzle 21 a _(n) after the (N−1)th droplet is sprayed for a pre-determined (N−1) time duration. The first droplet, the second droplet, the third droplet, . . . and the Nth droplet may be aligned as a row of droplets. In one embodiment, the first time duration, the second time duration, the third time duration . . . , and the (N−1)th time duration are same; and may be equal to the first time duration.

Thus, after the first droplet sprayed through the first spray nozzle 21 a ₁ arrives at the irradiating position 202 for the first time duration, the second droplet sprayed through the second spray nozzle 21 a ₂ may arrive at the irradiating position 202; after the second droplet arrives the irradiating position 202 for the first time duration, the third droplet sprayed through the third spray nozzle 21 a ₃ may arrive at the irradiating position 202, . . . ; and after the (N−1)th droplet sprayed through the (N−1)th spray nozzle 21 a _(n-1) arrives at the irradiating position 202, the Nth droplet may arrive at the irradiating position 202.

Referring to FIG. 3 and FIG. 4, when the plurality of spray nozzles 21 (21 a ₁˜21 a _(n)) are spraying the plurality of droplets 22, the laser source 203 may cause the generated first laser beam 31 or second laser beam 32 to scan along the scanning direction 200, the first laser beam 31 or the second laser beam 32 may sequentially bombard the first droplet, the second droplet, the third droplet, . . . , and the Nth droplet arriving at the irradiating position 202. Using the first laser beam 31 as an example, a specific process may include following steps. After the first laser beam 31 generated by the laser source 203 bombards the first droplet 22 at the irradiating position 202, the laser source 203 may cause the first laser beam 31 to scan along the scanning direction 200.

When the second droplet 22 arrives at the irradiating position 202, the first laser beam 31 may bombard the second droplet arriving at the irradiating position 202. Then, the laser source 203 may cause the first laser beam 31 to continuously scan along the scanning direction 200. When the third droplet 22 arrives at the irradiating position 202, the first laser beam 31 may bombard the third droplet 22 at the irradiating position 202. Then, the laser source 203 may cause the first laser beam 31 to continuously scan . . . . When the Nth droplet arrives at the irradiating position 202, the first laser beam 31 may bombard the Nth droplet at the irradiating position 202.

When the first droplet, the second droplet, the third droplet, . . . , and the Nth droplet are sequentially bombarded by the first laser beam 31, plasma may be generated correspondingly. The generated plasma may irradiate EUV light. At the same time, the light focusing device 215 may perform a rotating scan to sequentially collect the EUV light; and focus the collected EUV light at the central focusing point 220.

Specifically, after the light focusing device 215 collects the EUV light generated by bombarding the first droplet, and focuses the collected EUV light at the central focusing point 220, the light focusing device 215 may perform a rotating scanning; and collect the EUV light generated by bombarding the second droplet; and focus the collected EUV light at the central focusing point 220. Then, the light focusing device 215 may continue to perform a rotation scanning; and collect the EUV light generated by bombarding the third droplet; and focus the collected EUV light at the central focusing point 220 . . . . Then, the light focusing device 215 may continue to perform a rotating scanning; and collect EUV light generated by bombarding the Nth droplet; and focus the collected EUV light at the central focusing point 220.

Further, referring to FIG. 4, in one embodiment, a process for the first spray nozzle 21 a ₄, the second spray nozzle 21 a ₂, the third spray nozzle 21 a ₃, . . . , and the Nth (N≧3) spray nozzle 21 a _(n) of the spray nozzle array 201 to spray a plurality of droplets 22 downwardly to the irradiating position 202 may include: spraying a first drop of first droplet through the first spray nozzle 21 a ₁; spraying a first drop of second droplet through the second spray nozzle 21 a ₂ after the first drop of first droplet is sprayed for a first time duration; spraying a first drop of third droplet through the third spray nozzle 21 a ₃ after the first drop of second droplet is sprayed for the first time duration, . . . ; and spraying a first drop of Nth droplet through the Nth spray nozzle 21 a _(n) after the first drop of (N−1)th droplet is sprayed for the first time duration.

Further, after the first spray nozzle 21 a ₁ sprays the first drop of first droplet, a second drop of first droplet, a third drop of first droplet, a fourth drop of first droplet, . . . , and an Mth (M≧4) drop of first droplet may be sequentially sprayed through the first spray nozzle 21 a ₁ with a time interval of a second time duration. Similarly, after the second spray nozzle 21 a ₂ sprays the first drop of second droplet, a second drop of second droplet, a third drop of second droplet, a fourth drop of second droplet, . . . , and an Mth (M≧4) drop of second droplet may be sequentially sprayed from the second spray nozzle 21 a ₂ with a time interval of the second time duration.

Similarly, after the third spray nozzle 21 a ₃ sprays the first third droplet, a second drop of third droplet, a third drop of third droplet, a fourth drop of third droplet, . . . , and an Mth (M≧4) drop of third droplet may be sequentially sprayed for the third spray nozzle 21 a ₃ with a time interval of the second time duration . . . . Similarly, after the Nth spray nozzle 21 a _(n) sprays the first drop of Nth droplet, a second drop of Nth droplet, a third drop of Nth droplet, a fourth Nth droplet 22, . . . , and an Mth (M≧4) drop of Nth droplet 22 may be sequentially sprayed from the Nth spray nozzle 21 a _(n) with a time interval of the second time duration.

The first drop of first droplet, the first drop of second droplet, the first drop of third droplet, . . . , and the first drop of Nth droplet may form a first row of droplets 22; the second drop of first droplet, the second drop of second droplet, the second drop of third droplet, . . . , and the second drop of Nth droplet may form a second row of droplets 22; the third drop of first droplet, the third drop of second droplet, the third drop of third droplet, . . . , and the third drop of Nth droplet may form the third row of droplets 22; . . . ; and the Mth drop of first droplet, the Mth drop of second droplet, the Mth drop of third droplet, . . . , the Mth drop of Nth droplet may form the Mth row of droplets 22. The adjacent rows of droplets 22 may be parallel.

Such a method for spraying the plurality of rows of droplets 22 may regularly (e.g. adjacent droplets 22 may have a same interval, and adjacent rows of droplets 22 have a same interval) and continuously spray droplets 22 to the irradiating position 202. Thus, the supplying quantity of the droplets 22 per unit time may be increased. Further, such a method for spraying the plurality of rows of droplets 22 may also cause the first laser beam 31 or the second laser beam 32 generated by the laser source 203 to regularly scan along the scanning direction 200. Thus, the first laser beam 31 and the second laser beam 32 may sequentially bombard the plurality of rows of droplets 22 at the irritating position 202. Then, the light focusing device 215 may regularly perform a rotating scanning to collect the irradiating EUV light; and focus the collected EUV light at the central focusing point 220. Thus, the power of the EUV light at the central focusing point 220 may be increased.

Further, referring to FIG. 4, the first drop of first droplet and the second drop of first droplet may have a first distance “S”; the first drop of second droplet and the second drop of second droplet may have a first distance “S”; the first drop of third droplet and the second drop of third droplet may have a first distance “S”; . . . ; and the first drop of Nth droplet and the second drop of Nth droplet may have a first distance “S”. In one embodiment, the first distance “S” may be in a range of approximately 45 μm˜75 μm.

Further, the first drop of first droplet and the first drop of second droplet along the “Z” direction may have a second distance “H1”; the first drop of second droplet and the first drop of third droplet along the “Z” direction may have a second distance “H1”; . . . ; and the first drop of (N−1)th droplet and the first drop of Nth droplet along the “Z” direction may have second distance “H1”. The second drop of first droplet and the second drop of second droplet along the “Z” direction may have a second distance “H1”; the second drop of second droplet and the second drop of third droplet along the “Z” direction may have a second distance “H1”; . . . ; and the second drop of (N−1)th droplet and the second drop of Nth droplet along the “Z” direction may have the second distance “H1”. The third drop of first droplet and the third drop of second droplet along the “Z” direction may have the second distance “H1”; the third drop of second droplet and the third drop of third droplet along the “Z” direction may have the second distance “H1”; . . . ; and the third drop of (N−1)th droplet and the third drop of Nth droplet along the “Z” direction may have the second distance “H1” . . . . The Mth drop of first droplet and the Mth drop of second droplet along the “Z” direction may have a second distance “H1”; the Mth drop of second droplet and the Mth drop of third droplet along the Z direction may have the second distance “H1”; . . . ; and the Mth drop of (N−1)th droplet and the Mth drop of Nth droplet along the “Z” direction may have the second distance “H1”.

Further, referring to FIG. 3, the laser source 203 may include a laser 204; a reflective mirror 209, and a second driving device (not labeled). The laser 204 may be configured to generate a laser beam. The reflective mirror 209 may configured to reflect the laser beam; and cause the laser beam to irradiate the irradiating position 202. The second driving device may be connected with the reflective mirror 209 to drive the reflective mirror 209 to rotate such that the laser beam reflected by the reflective mirror 209 may scan along the scanning direction 200; and may sequentially bombard the droplets 22 at the irradiating position 202.

The laser 204 may be a pumped laser with a relatively high pulse frequency. Thus, the laser beam may bombard more droplets 22 per unit time. The pumped laser may be Q-switched laser, or a mode-locked laser, etc. In one embodiment, the laser 204 is a CO₂ laser. The output power of the laser 204 may be in a range of approximately 10 kW˜200 kW.

The pulse irradiation of the laser 204 may synchronize with the spraying of the droplets 22 and the rotating scanning of the reflective mirror 209 and the light focusing mirror 214. By doing so under the control signals from a controller (not shown), when the droplets 22 arrive the irritating position 202, the corresponding laser beam may be able to bombard the droplets 22; and the reflective mirror 209 may collect the EUV light irradiated from the droplets 22 and focus the collected EUV light at the central focusing point 220.

Referring to FIG. 3, in one embodiment, the reflective mirror 209 may include a first reflective mirror 207 and a second reflective mirror 208; and the first reflective mirror 207 and the second reflective mirror 208 may be separated. The second driving device may include a third sub-driving device 205 and a fourth sub-driving device 206. The first reflective mirror 207 may be disposed above the second reflective mirror 208. The first reflective mirror 207 may reflect a portion of the laser beam to form the first laser beam 31. The third sub-driving device 205 may be connected with the first reflective mirror 207. Further, the third sub-driving device 205 may drive the first reflective mirror 207 to rotate to cause the first laser beam 31 to scan along the scanning direction 200 to sequentially bombard the droplets 22 at the irradiating position 202.

The second reflective mirror 208 may reflect a portion of the laser beam to form the second laser beam 32. The fourth sub-driving device 206 may be connected with the second reflective mirror 208. Further, the fourth sub-driving device 206 may drive the second reflective mirror 208 to rotate to cause the second laser beam 32 to scan along the scanning direction 200 to sequentially bombard the droplets 22 at the irradiating position 202.

The third sub-driving device 205 may be disposed above the first reflective mirror 207; and may be connected with the first reflective mirror 207 by a bearing. The fourth sub-driving device 206 may be disposed below the second reflective mirror 208; and may be connected with the second reflective mirror 208 by a hearing. The bearings may be electromagnetic bearings, or mechanical bearings, etc.

The third sub-driving device 205 may drive the first reflective mirror 207 by any appropriate methods, such as an electromagnetic drive method, or a piezoelectric drive method. The fourth sub-driving device 206 may drive the second reflective mirror 208 by any appropriate methods, such as an electromagnetic drive method, or a piezoelectric drive method.

The third sub-driving device 205 and the fourth sub-driving device 206 may include power supplies (not shown) and driving circuitry (not shown), etc. The power supplies may provide power for driving the first reflective mirror 207 and the second reflective mirror 208 to rotate. The driving circuitry may provide drive signals to the power supplies. The power supplies may be electric motors, etc.

Further, a lens unit 219 may be disposed in the optical path between the laser 204 and the first reflective mirror 207, and the optical path between the laser 204 and the second reflective mirror 208. The lens unit 219 may be configured to adjust the incident angle of the laser beam to the first reflective mirror 207 and the second reflective mirror 208 when the laser beams generated by the laser 204 irradiate the first reflective mirror 207 and the second reflective mirror 208. The adjustment may cause the first laser beam 31 reflected by the first reflective mirror 207 and the second laser beam 32 reflected by the second reflective mirror 208 to be able to reach the irradiating position 202.

According to the disclosed embodiments, the first laser beam 31 and the second laser beam 32 may be able to alternately bombard different rows of droplets 22 arriving at the irradiating position 202. When a relative large number of droplets 22 per unit time arrive at the irradiating position 202, for example, the second time duration may be substantially short causing the number of the droplets 22 to increase, the first laser beams 31 and the second laser beam 32 may alternately scan to bombard the different rows of droplets 22 arriving at the irradiating position 202. Thus, the power of the irradiated EUV light may be increased.

In one embodiment, a process for the first laser beam 31 and the second laser beam 32 alternately bombarding the different rows of droplets 22 at the irradiating position 202 may include following steps. First, when the Lth (L≧1) row of droplets 22 arrive at the irradiating position 202, the third sub-driving device 205 drives the first reflective mirror 207 to rotate from an initial position to cause the first laser beam 31 reflected by the first reflective mirror 207 to scan along the scanning direction 200 to sequentially bombard the Lth row of droplets 22 at the irradiating position 202.

After bombarding the Lth row of droplets 22, the third sub-driving device 205 may drive the first reflective mirror 207 back to the initial position. Then, when the (L+1)th row of droplets 22 arrive at the irradiating position 202, the fourth sub-driving device 206 may drive the second reflective mirror 208 to rotate from an initial position to cause the second laser beam 32 reflected by the second reflective mirror 208 to scan along the scanning direction 200 to sequentially bombard the (L+1)th row of droplets 22.

After bombarding the (L+1)th row of droplets 22 arriving at the irradiating position 202, the fourth sub-driving device 206 may drive the second reflective mirror 208 back to the original position. Then, when the (L+2)th row of droplets 22 arrive at the irradiating position 202, the third sub-driving device 205 may drive the first reflective mirror 207 to rotate from the initial position to cause the first laser beam 31 reflected by the first reflective mirror 207 to scan along the scanning direction 200 to sequentially bombard the (L+2)th row of droplets 22 arriving at the irradiating position 202.

After bombarding the (L+2)th row of droplets 22, the third sub-driving device 205 may drive the first reflective mirror 207 back to the initial position. Then, when the (L+3)th row of droplets 22 arrive at the irradiating position 202, the fourth sub-driving device 206 may drive the second reflective mirror 208 to rotate from the initial position to cause the second laser beat 32 reflected by the second reflective mirror 208 to scan along the scanning direction to sequentially bombard the (L+3)th row of droplets 22.

After bombarding the (L+3)th row of droplets 22 at the irradiating position 202, the fourth sub-driving device 206 may drive the second reflective mirror 208 back to the original position. Such steps may be repeated to generate continuous EUV light.

In certain other embodiments, a process for the first laser beam 31 and the second laser beam 31 to alternately bombard the different rows of droplets 22 at the irradiating position 202 may include following steps. First, when the Lth (L≧1) row of droplets 22 arrive at the irradiating position 202, the fourth sub-driving device 206 may drive the second reflective mirror 208 to rotate from an initial position to cause the second laser beam 32 reflected by the second reflective mirror 208 to scan along the scanning direction 200 to sequentially bombard the Lth row of droplets 22 at the irradiating position 202.

After bombarding the Lth row of droplets 22, the fourth sub-driving device 206 may drive the second reflective mirror 208 back to the initial position. Then, when the (L+1)th row of droplets 22 arrive at the irradiating position 202, the third sub-driving device 205 may drive the first reflective mirror 207 to rotate from an initial position to cause the first laser beam 31 reflected by the first reflective mirror 207 to scan along the scanning direction to sequentially bombard the (L+1)th row of droplets 22.

After bombarding the (L+1)th row of droplets 22 at the irradiating position 202, the third sub-driving device 205 may drive the first reflective mirror 207 back to the original position. Then, when the (L+2)th row of droplets 22 arrive at the irradiating position 202, the fourth sub-driving device 206 may drive the second reflective mirror 208 to rotate from the initial position to cause the second laser beam 32 reflected by the second reflective mirror 208 to sequentially scan along the scanning direction 200 to sequentially bombard the (L+2)th row of droplets 22 at the irradiating position 202.

After bombarding the (L+2)th row of droplets 22, the fourth sub-driving device 206 may drive the second reflective mirror 208 back to the initial position. Then, when the (L+3)th row of droplets 22 arrive at the irradiating position 202, the third sub-driving device 205 may drive the first reflective mirror 207 to rotate from an initial position to cause the first laser beam 31 reflected by the first reflective mirror 207 to sequentially scan along the scanning direction 207 to sequentially bombard the (L+3)th row of droplets 22.

After bombarding the (L+3)th row of droplets 22 at the irradiating position 202, the third sub-driving device 205 may drive the first reflective mirror 207 back to the original position. Such steps may be repeated to generate continuous EUV light.

In one embodiment, the first laser beam 31 may bombard the first row of droplets 22; the second laser beam 32 may bombard the second row of droplets 22; and then the first laser beam 31 may continue to bombard the third row of droplets 22; and then the second laser beam 32 may continue to bombard the fourth row of the droplets 22, and . . . . Specifically, when the first droplet in the first row arrives at the irradiating position 202, the first reflective mirror 207 may be at the initial position. A portion of the laser beam generated by the laser source 203 may be reflected by the first reflective mirror 207 to form the first laser beam 31; and the first laser beam 31 may irradiate to the irradiating position 202 to bombard the first drop of first droplet at the irradiating position 202.

Then, other droplets in the first row of droplets 22 may sequentially arrive at the irradiating position 202 with a time interval of the first time duration. Correspondingly, the first reflective mirror 207 may rotate driven by the third driving device 205. Thus, under the reflection of the first reflective mirror 207, the first laser beam 31 may scan along the scanning direction 200; and may sequentially bombard the other droplets in the first row.

After the last drop of the first row of droplets 22 is bombarded by the first laser beam 31, the first reflective mirror 207 may reach a stop position; and then the first reflective mirror 207 may be driven back to the initial position by the third sub-driving device 205. When the first droplet in the second row of droplets 22 arrives at the irradiating position 202, the second reflective mirror 208 may be at the initial position. A portion of the laser beam generated by the laser source 203 may be reflected by the second reflective mirror 208 to form the second laser beam 32; and the second laser beam 32 may irradiate to the irradiating position 202 to bombard the first droplet in the second row of droplets 22 at the irradiating position 202.

Then, other droplets 22 in the second row may sequentially arrive at the irradiating position 202 with a time interval of the first time duration. Correspondingly, the second reflective mirror 208 may rotate driven by the fourth driving device 206. Thus, under the reflection of the second reflective mirror 208, the second laser beam 32 may scan along the scanning direction 200; and may sequentially bombard the other droplets in the second row.

After the last droplet in the second row of droplets 22 is bombarded by the second laser beam 32, the second reflective mirror 208 may reach a stop position; and then the second reflective mirror 208 may be driven back to the initial position by the fourth sub-driving device 206. Then, when the third row of droplets 22 sequentially arrive at the irradiating position 202, the first laser beam 31 may scan along the scanning direction 200 to sequentially bombard the third row of droplets 22 arriving at the irradiating position 202.

After the last droplet in the third row is bombarded, the first reflective mirror 207 may rotate back to the initial position 202. Then, when the fourth row of droplets 22 sequentially arrive at the irradiating position 202, the second laser beam 32 may scan along the scanning direction 200 to sequentially bombard the fourth row of the droplets 202 at the irradiating position. After the last drop of the fourth row of droplets 202 is bombarded, the second reflective mirror 208 may be rotated back to the original position. Such steps may be repeated the last droplet in the last row of droplets 22 is bombarded.

To avoid mutual adverse effects between the first laser beam 31 and the second laser beam 32 or the adverse effects of the first laser beam 31 and/or the second laser beam 32 when the first laser beam 31 or the second laser beam 32 bombard the droplets 22, a first optical shutter 210 may be disposed between the first reflective mirror 207 and the irradiating position 202. The first optical shutter 210 may be configured to control the irradiation of the first laser beam to the irradiating position 202. Further, a second optical shutter 211 may be disposed between the second reflective mirror 208 and the irradiating position 202. The second optical shutter 211 may be configured to control the radiation of the second laser beam 32 to the irradiating position 202.

The first optical shutter 210 may include a first blocking unit (not shown) and a third driving device (not shown) connected with the first blocking unit. The second optical shutter 211 may include a second blocking unit and a fourth driving device connected with the second blocking unit. The third driving device may be configured to drive the first blocking unit to be on, or be away from the optical path of the first laser beam 31 to the irradiating position 202. The fourth driving device may be configured to drive the second blocking unit to be on, or away from the optical path of the second laser beam 32 to the irradiating position 202.

Thus, when the first laser beam 31 is bombarding the droplet 22 at the irradiating position 202, the fourth driving device may drive the second blocking unit to be on the optical path to the irradiating position 202; and the second laser beam 32 may be prevented from irradiating the irradiating position 202. When the second laser beam 32 is bombarding the droplets 22 at the irradiating position 202, the fourth driving device may drive the second blocking unit to be away from the optical path of the second laser beam 32 to the irradiating position 202; and the second laser beam 32 may irradiate the irradiating position 202.

At the same time, when the second laser beam 32 is irradiating the droplets 22 at the irradiating position 202, the third driving device may drive the first blocking unit to be on the optical path of the first laser beam 31 to the irradiating position 202; and the first laser beam 31 may be prevented from irradiating the irradiating position 202. When it is the turn for the first laser beam 31 to bombard the droplets 22 at the irradiating position 202 again, the third driving device may drive the first blocking unit to be away from the optical path of the first laser beam to the irradiating position 202. Thus, the first laser beam 31 may irradiate the irradiating position 202 to bombard the droplets 22 at the irradiating position 202.

Specifically, FIG. 5 illustrates exemplary structures of a first optical shutter 210 and a second optical shutter 211 according to the disclosed embodiments. As shown in FIG. 5, the first optical shutter 210 may include a first blocking unit 210 b and a third driving device 210 a connected with the first blocking unit 210 b; and the second optical shutter 211 may include a second blocking unit 211 b and a fourth driving device 211 a connected with the second blocking unit 211 b. In one embodiment, the first blocking unit 210 b may be a third reflective mirror.

When the third reflective mirror is blocking the first laser beam 31, the third reflective mirror may reflect the first laser beam 31 to a direction away for the second optical shutter 211 (or the positive direction of the z-axis). The second blocking unit 211 b may be a fourth reflective mirror. When the fourth reflective mirror is blocking the second laser beam 32, the fourth reflective mirror may reflect the second laser beam 32 to a direction away from the first optical shutter 210 (or the negative direction of the z-axis).

In certain other embodiments, the first blocking unit 210 b may reflect the first laser beam 31 to the positive direction or the negative direction of the x-axis. The second blocking unit 211 b may reflect the second laser beam 32 to the positive direction or the negative direction of the x-axis.

Further, a first heat recycling unit (not shown) may be disposed on the irradiating direction of the first laser beam 31 reflected by the third reflective mirror. The first heating recycling unit may be configured to absorb the first laser beam 31 reflected by the third reflective mirror. A second heat recycling unit (not shown) may be disposed on the irradiating direction of the second laser beam 32 reflected by the fourth reflective mirror. The second heating recycling unit may be configured to absorb the second laser beam 32 reflected by the fourth reflective mirror. The absorption of the reflected first laser beam 31 and the reflected second laser beam 32 may prevent the first laser beam 31 and the second laser beam 32 from being reflected for a second time.

Further, reaming to FIG. 3, the light focusing device 215 may be disposed between the reflective mirror 209 and the irradiating position 202. The light focusing device 215 may include a focusing mirror (not labelled) and a first driving device. The focusing mirror may have an elliptical reflective surface facing the irradiating position 202. The elliptical reflective surface may collect the irradiated EUV light; and focus the collected EUV light at the central focusing point 220. The first driving device may be connected with the focusing mirror; and may be configured to drive the focusing mirror to perform rotating scanning. When the first laser beam 31 or the second laser beam 32 sequentially bombard the droplets arriving at the irradiating position 202 to generate the irradiating EUV light, the focusing mirror may collect the irradiated the EUV light; and focus the collected light at the central focusing point 220.

Further, a channel 218 may be disposed at the center of the focusing mirror. The channel 218 may cause the laser beam reflected by the reflective mirror 209 to pass through to irradiate the droplets 22 arriving at the irradiating position 202. In one embodiment, the channel 208 is a through-hole.

The focusing mirror may include a top focusing mirror 212 and a bottom focusing mirror 213. The top focusing mirror 212 and the bottom focusing mirror 213 may be separated. Further, the top focusing mirror 212 may be disposed above the bottom focusing mirror 213. The top focusing mirror 212 may include at least two first sub-focusing mirrors 212 a; and the bottom focusing mirror 213 may include at least two second sub-focusing mirrors 213 a. The first driving device may include at least two first sub-driving devices 216 a; and at least two second sub-driving device 217 a. Each of the at least two first sub-driving device 216 a may be connected with a first sub-focusing mirror 212 a; and each of the at least two second sub-driving device 217 a may be connected with a second sub-focusing mirror 213 a. The at least two first sub-driving device 216 a and the corresponding at least two first sub-focusing mirrors 212 a may perform rotating scanning simultaneously; and the at least two second sub-driving device 217 a and the corresponding at least two second sub-focusing mirror 213 a may perform rotating scanning simultaneously.

In one embodiment, the focusing mirror is separated by the plane having the central focusing point 220 and the irradiating position 202 into the top focusing mirror 212 and the bottom focusing mirror 213. The top focusing mirror 212 may include the at least two separated first sub-focusing mirror 212 a; and the bottom focusing mirror 213 may include the at least two separated second sub-focusing mirrors 213 a.

In one embodiment, the top focusing mirror 212 and the bottom focusing mirror 213 may be formed by separating or cutting an entire elliptical surface. Then, the at least two separated first sub-focusing mirrors 212 a may be formed by separating or cutting the top focusing mirror 212. Then, the at least two separated second sub-focusing mirrors 213 a may be formed by separating or cutting the bottom focusing mirror 213.

In one embodiment, there may be a first separating plane (not labelled) between the top focusing mirror 212 and the bottom focusing mirror 213. The first separating plane may refer to the plane separating the op focusing mirror 212 and the bottom focusing mirror 213, or the plane having the central focusing point 220 and the irradiating position 202. The top focusing mirror 212 and the bottom focusing mirror 213 may be symmetric to the first separating plane.

There may be a second separating plane between adjacent first sub-focusing mirrors 212 a. The second separating plane may refer to a plane for separating the adjacent first sub-focusing mirrors 212 a. The second separating plane may be perpendicular to the first separating plane. Further, there may be a third separating plane between adjacent second sub-focusing mirrors 213 a. The third separating plane may refer to a plane separating the adjacent second sub-focusing plane 213 a. The third separating plane may be perpendicular to the first separating plane.

In certain other embodiments, the top focusing mirror 212 may be separated into at least two first sub-focusing mirrors 212 a by a plurality of second separating planes; and the bottom focusing mirror 213 may be separated into at least two second sub-focusing mirror 213 a by a plurality of third separating planes. The at least two first sub-focusing mirrors 212 a and the at least two second sub-focusing mirrors 213 a may have same angles, same masses, and/or same areas.

In one embodiment, the number of the first sub-focusing mirrors 212 a and the number of the second sub-focusing mirrors 213 a may be identical. The number of the first sub-driving device 216 a and the number of the second sub-driving device 217 a may be identical. Each of the first sub-focusing mirrors 212 a may be connected with a corresponding second sub-driving device 216 a; and each of the second sub-focusing mirrors 213 a may be connected with a corresponding second sub-driving device 217 a.

The first sub-driving device 216 a and the second sub-driving device 217 a may include driving circuitry, power supplies, axis and bearings. The power supplies may be connected with one end of the axis; and the other end of the axis may be connected and fixed with the back of the first sub-focusing mirror 212 a and the back of the sub-focusing mirror 213 a. The power supplies may provide power for the rotation of the top focusing mirror 212 and the bottom focusing mirror 213. The driving circuitry may provide drive signals to the power supplies. The power supplies may be electric motor, etc. The bearings may be electromagnetic bearings, or mechanical bearings, etc.

In one embodiment, the focusing mirror is elliptically shaped. The top focusing mirror 212 and the bottom focusing mirror 213 may be semi-elliptical surface. The top focusing mirror 212 may include a plurality of separated first sub-focusing mirrors 212 a; and the plurality of separated first sub-focusing mirrors 212 a may be sequentially aligned into the semi-elliptical surface. Each of the plurality of separated first sub-focusing mirrors 212 a may be connected with a corresponding first sub-driving device 216 a. The plurality of first sub-driving device 216 a may drive the plurality of first sub-focusing mirrors 212 a to perform rotating scanning simultaneously.

During the rotating scanning process, the relatively position of adjacent first sub-focusing mirrors 212 a may remain the same. The bottom focusing mirror 213 may include a plurality of separated second sub-focusing mirrors 212 a; and the plurality of separated second sub-focusing mirrors 213 a may be sequentially aligned into the semi-elliptical surface. Each of the plurality of separated second sub-focusing mirrors 213 a may be connected with a corresponding second sub-driving device 217 a. The plurality of second sub-driving device 217 a may drive the plurality of second sub-focusing mirrors 213 a to perform rotating scanning simultaneously. During the rotating scanning process, the relatively position of adjacent second sub-focusing mirrors 213 a may remain the same.

In one embodiment, a portion of the laser beam generated from the light source 203 may be reflected by the first reflective mirror 207 to form the first laser beam 31; and a portion of the laser beam generated from the light source 203 may be reflected by the second reflective mirror 208 to form the second laser beam 32. The first laser beam 31 and the second laser beam 32 may scan along the second direction 200 to bombard different rows of droplets 22. The first sub-driving device 216 a and the second sub-driving device 217 a may be able to respectively drive th top focusing mirror 212 and the bottom focusing mirror 213 to perform rotating scanning to collect the EUV light generated by the bombarding different rows of droplets 22 using the first laser beam 31 and the second laser beam 32.

Specifically, when the first laser beam 31 scans along the scanning direction 200 to bombard a certain row of the droplets 22 arriving at the irradiating position 202, the top focusing mirror 212 may be driven by the first sub-driving device 216 a to perform rotating scanning to collect EUV light generated by bombarding the certain row of droplets 22 using the laser beam 31; and focus the collected EUV light at the central focusing point 220. When the second laser beam 32 scans along the scanning direction 200 to bombard a next row of droplets 22 arriving at the irradiating position 202, the bottom focusing mirror 213 may be driven by the second sub-driving device 217 a to perform rotating scanning to collect EUV light generated by bombarding the row of the droplets 221, and focus the collected EUV light at the central focusing point 220.

The rotating scanning of the top focusing mirror 212 and the rotating scanning of the first reflective mirror 207 may be synchronized. The rotating scanning of the bottom focusing mirror 213 and the rotating scanning of the second reflective mirror 208 may be synchronized.

Further, the EUV light source may also include a control unit (not labelled). The control unit may provide synchronized first signals, second signals, and third signals. The first signals may control the spray nozzles 21 to sequentially spray droplets. The second signals may control the first driving device to drive the reflective mirror to rotate synchronically. The third signals may control the second driving device to drive the focusing mirror to rotate synchronically.

Further, the EUV light source may also include a cleaning system (not shown). The cleaning system may be configured to clean contaminations on the reflective mirror of the focusing mirror, such as the pieces generated when the droplets are bombarded.

FIG. 6 illustrates an exemplary control signal graph according to the disclosed embodiments as shown in FIG. 6, the first signals may include a first sub-first signal 31 a ₁, a second sub-first signal 31 a ₂, a third sub-first 31 a ₃ . . . ; and an Nth sub-first signal 31 a _(n). The second signals may include a first sub-second signal 305 and a second sub-second-signal 306. The third signals may include a first sub-third signal 316 and a second sub-third signal 317.

The first signals, the second signals and the third signals may be generated from a same clock. The number of the first signals may be identical to the number of the first spray nozzles 21. The first sub-first signal 31 a ₁, the second sub-first signal 31 a ₂. The third sub-first 31 a ₃ . . . ; and the Nth sub-first signal 31 a, may respectively control the on/off of the switches corresponding to the first spray nozzle 21 a ₁, the second spray nozzle 21 a ₂, the third spray nozzle 21 a ₃ . . . , and the Nth spray nozzle 21 a _(n) (referring to FIG. 4).

The first sub-second signal 305 may be configured to control the first sub-driving device 205 to drive the first reflective mirror 207 to rotate during “scanning” and to reset to its initial position during “resetting.” The second sub-second signal 206 may be configured to control the second driving device 206 to drive the second reflective mirror 208 to rotate during “scanning” and to reset to its initial position during “resetting.” The first sub-third signal 316 may be configured to control the third sub-driving device to drive the top focusing mirror 212 to rotate during “scanning” and to reset to its initial position during “resetting.” The second sub-third signal 317 may be used to control the fourth sub-driving device 217 a to drive the bottom focusing mirror 213 to rotate during “scanning” and to reset to its initial position during “resetting.”

FIGS. 7˜8 illustrate the structures corresponding certain stages of a process for using the EUV light source to generate EUV light according to the disclosed embodiments. The control signals illustrated in FIG. 6 may be used to control the EUV light source.

As shown in FIG. 6, the first sub-first signal 31 a ₁, the second sub-first signal 31 a ₂, the third sub-first 31 a ₃ . . . , and the Nth sub-first signal 31 a _(n) may be pulse signals. The time interval between adjacent pulses may be referred as a second time T2. Further, the second sub-first signal 31 a ₂ may lag behind the first sub-first signal 31 a ₁ for a first time T1; the third sub-first signal 31 a ₃ may lag behind the second sub-first signal 31 a ₂ for the first time T1; . . . ; and the Nth sub-first signal 31 a _(n) may lag behind the (N−1)th sub-first signal 31 a _(n-1) for the first time T1.

Further, the first signals may match a relationship of N≧T1=T2, wherein “N” refers to the number of the first signals (or the number of the spray nozzles 21); T1 refers to the first time; and T2 refers to the second time. Such a relationship may cause the first laser beam 31 and the second laser beam 32 to alternately bombard different rows of droplets 22 at the irradiating position 202.

Thus, when the first sub-first signal 31 a ₁, the second sub-first signal 31 a ₂, the third sub-first 31 a ₃ . . . ; and the Nth sub-first signal 31 a are applied on the switches corresponding to the plurality of spray nozzles 21 (the first spray nozzle 21 a ₁, the second spray nozzle 21 a ₂, the third spray nozzle 21 a ₃ . . . , and the Nth spray nozzle 21 a illustrated in FIG. 3), the spray nozzle array 201 may sequentially spray a plurality of rows of droplets 22, such as the first row of droplets 22, the second row of droplets 22, the third row of droplets 22, . . . , and the Mth (M≧3) row of droplets 22, downwardly to the irradiating position 22.

Each row of droplets 22 may include a drop of first droplet 2 sprayed by the first spray nozzle 21 a ₁, a drop of second droplet 22 sprayed by the second spray nozzle 21 a ₂ lagging behind the first spray nozzle 21 a ₁ for the first time T1; a drop of third droplet sprayed by the third spray nozzle 21 a ₃ lagging behind the second spray nozzle 21 a, for the first time T1; . . . ; and a drop of Nth droplet sprayed by the Nth spray nozzle 21 a _(n) lagging behind the (N−1)th spray nozzle 21 a _(n-1) for the first time T1. Further, the time interval between adjacent rows of droplets 22 may be equal to the second time T2.

Reaming to FIG. 6, before the spray nozzle array 21 sprays the droplets 22, the first reflective mirror 207 and the second reflective mirror 208 may be both at a first initial position. The top focusing mirror 212 and the bottom focusing mirror 213 may be at a third initial position. When the first droplet (sprayed from the first spray nozzle 21 a ₁) arrives at the irradiating position 202, the first reflective mirror 207 may be driven by the third sub-driving device 205 to accelerate from the first initial position to a second initial position; or the second reflective mirror 208 may be driven by the fourth sub-driving device 206 to accelerate from the first initial position to the second initial position.

When the first reflective mirror 207, or the second reflective mirror 208 is at the second initial position, the first laser beam 31 reflected by the first reflective mirror 207 or the second laser beam 32 reflected by the second reflective mirror 208 may be able to bombard the first droplet arriving at the irradiating position 202. At the same time, the top focusing mirror 212 or the bottom mirror 213 may be driven by the first sub-driving device 216 a or the second sub-driving device 217 a to accelerate from the third initial position to a fourth initial position.

When the top focusing mirror 212 or the bottom focusing mirror 213 are at the fourth initial position, the top focusing mirror 212 or the bottom focusing mirror may collect the EUV light generated by bombarding the first droplet; and focus the collected EUV light at the central focusing point 202.

For illustrative purposes, the first laser beam 31 may bombard the first row of droplets 22 arriving at the irradiating position 202; and the second laser beam 32 may continue to the bombard the second row of droplets 22 arriving at the irritating position 202. The corresponding second signals and the corresponding third signals may be referred to FIG. 6. In certain other embodiments, the second laser beam 32 may be used to bombard the first row of droplets 22 arriving at the irradiating position 202; and the first laser beam 31 may be used to bombard the second row of droplets 22 arriving at the irradiating position 202.

As shown in FIG. 6, the first sub-second signal 305 may include alternative scanning stages and resetting stages. The starting point of the first scanning stage of the first sub-second signal 305 may lag behind the first pulse of the first sub-first signal 31 a ₁ for a third time 13. The third time 13 may be equal to the time duration between the first spray nozzle 21 a ₁ starts to spray a first drop of first droplet 22 and the first drop of first droplet 22 arrives at the irradiating position 202. The ending time of the first scanning stage of the first sub-second signal 305 may lag behind the first pulse of the Nth sub-first signal 31 a for a fourth time T4.

The fourth time T4 may be equal to the time duration between the Nth spray nozzle 21 a _(n) starts to spry the first drop of Nth droplet 22 and the first drop of Nth droplet 22 arrives at the irradiating position 202. The first resetting stage may come right after the first scanning stage; and scanning stages and the adjacent resetting stages may have not time interval. The time of the scanning stage of the first sub-second signal 305 may be equal to the second time T2. The total time of each scanning stage and resetting stage may be smaller than two times of the second time T2. The time interval between the end of one scanning stage and the start of the adjacent next scanning stage may be equal to the second time T2.

The scanning stages of the first sub-second signal 305 may be configured to control the third sub-driving device 205 to drive the first reflective mirror 207 to rotate with a constant speed from the second initial position. The resetting stages of the first sub-second signal 305 may configured to control the third sub-driving device 205 to drive the first reflective mirror 207 to rotate back to the first initial position.

The first sub-second signal 305 may also include accelerating stage (not shown) before each scanning stage. The accelerating stage may be used to control the third sub-driving device 205 to drive the first reflective mirror 207 to accelerate from the first initial position to the second initial position.

Correspondingly, the first sub-third signal 316 may include alternative scanning stages and resetting stages. The first sub-third signal 316 may be synchronized with the third sub-second signal 305. That is, the starting time and the ending time of the scanning stage and the resetting stage of the first sub-third signal 316 may be identical to the starting time and the ending time of the scanning stage and the resetting stage of the first sub-second signal 205.

The scanning stages of the first sub-third signal 316 may be used to control the plurality of first sub-driving device 216 a to drive the top focusing mirror 212 to perform rotating scanning with a constant speed starting from a fourth initial position. The resetting stages of the first sub-third signal 316 may be used to control the plurality of first sub-driving device 216 a to drive the top focusing mirror to rotate back to the third initial position.

The first sub-third signal 316 may also include an accelerating stage (not shown) before each scanning stage. The accelerating stage may be used to control the plurality of first sub-driving device 216 a to drive the top focusing mirror 212 to accelerate from the third position to the fourth position.

Further, as shown in FIG. 6, the second sub-second signal 306 may also include alternative scanning stages and resetting stages. The starting point of the first scanning stage of the second sub-second signal 206 may lag behind the second pulse of the first sub-first signal 31 a ₁ for a fifth time T5. The fifth time T5 may be equal to the time duration between the first spray nozzle 21 a ₁ starts to spray a second drop of the first droplet 22 and the second drop of the first droplet 22 arrives at the irradiating position 202. The fifth time T5 may be equal to the third time T3. The ending time of the first scanning state of the second sub-second signal 206 may lag behind the second pulse of the Nth sub-first signal 31 a _(n) tier a sixth time T6. The sixth time T6 may be equal to the time duration between the Nth spray nozzle 21 a _(n) starts to spray the second drop of the Nth droplets and the second drop of the Nth droplets arrives at the irradiating position 202. The sixth time T6 may be equal to the fourth time T4.

The first resetting stage may come right after the first scanning stage; and scanning stages and the adjacent resetting stages may have not time interval. The time of the scanning stage of the second sub-second signal 206 may be equal to the second time T2. The total time of each scanning stage and resetting stage may be smaller than two times of the second time T2. The time interval between the end of one scanning stage and the start of the adjacent next scanning stage may be equal to the second time T2.

Further, the starting time of the first scan stage of the second sub-second signal 206 may come right after the ending time of the first scanning stage of the first sub-second signal 205. Thus, when the first laser beam 31 finishes bombarding a certain row of droplets 22 arriving at the irradiating position 202, the second laser beam 32 may start bombarding a next row of droplets 22 arriving at the irradiating position 202 right away.

Correspondingly, the second sub-third signal 317 may include alternative scanning stages and resetting stages. The second sub-third signal 317 may be synchronized with the second sub-second signal 306. That is, the starting time and the ending time of the scanning stage and the resetting stage of the second sub-third signal 317 may be identical to the starting time and the ending time of the scanning stage and the resetting stage of the second sub-second signal 306.

The scanning stages of the second sub-third signal 317 may be used to control the plurality of second sub-driving device 217 a to drive the bottom focusing mirror 213 to perform a rotating scanning with a constant speed starting from a fourth initial position. The resetting stages of the second sub-third signal 317 may be used to control the plurality of second sub-driving device 217 a to drive the bottom focusing mirror 213 to rotate back to the third initial position.

The second sub-third signal 317 may also include an accelerating stage (not shown) before each scanning stage. The accelerating stage may be used to control the plurality of second sub-driving device 217 a to drive the bottom focusing mirror 213 to accelerate from the third position to the fourth position.

In one embodiment, the total time of a scanning stage and a resetting of the first sub-second signal 305 may be smaller than two times of the second time T2. The total time of a scanning stage and a resetting of the second sub-second signal 306 may be smaller than two times of the second time T2. The total time of a scanning stage and a resetting of the first sub-third signal 316 may be smaller than two times of the second time T2. The total time of a scanning stage and a resetting of the second sub-third signal 317 may be smaller than two times of the second time T2.

As shown FIG. 7, specifically, after the spray nozzle array 21 receives the first signals 31 a ₁˜31 a _(n); the third sub-driving device 205 receives the first sub-second signal 305; the fourth sub-driving device 206 receives the second sub-second signal 306; the plurality of first sub-driving device 216 a receives the first sub-third signal 316; and the plurality of second sub-driving device 217 a receives the second sub-third signal 317, the droplet array 201 may spray a plurality of droplets 22 to the irradiating position 202, including a first row of droplets 21, a second row of droplets 22, a third row of droplets 22, . . . , and an Mth row of droplets 22.

When the first droplet 22 of the first row of droplets 22 arrives at the irradiating position 202, the third sub-apparatus 205 may drive the first reflective mirror 207 to accelerate from the first initial position to the second initial position; and the first laser beam 31 may bombard the first droplet 22 arriving at the irradiating position 202. At the same time, the plurality of first sub-apparatus 216 a may drive the top focusing mirror 212 to accelerate form the third initial position to the fourth initial position. The top focusing mirror 212 may collect the EUV light generated by bombarding the first droplet 22 of the first row of droplets 22; and focus the collected EUV light at the central focusing point 220.

Then, the first scanning stage of the first sub-second signal 305 may cause the third sub-driving device 205 to drive the first reflective mirror 207 to rotate with a constant speed starting from the third initial position. The first laser beam 31 may scan along the scanning direction 200 to bombard other droplets of the first row of droplets 22 sequentially arriving at the irradiating position 202.

At the same time, the first scanning stage of the first sub-third signal 316 may cause the plurality of first sub-driving device 216 a to drive the top focusing mirror 212 to rotate with a constant speed starting from the second initial position. During the rotating, the top focusing mirror 212 may sequentially collect the EUV light generated by bombarding other droplets 22 of the first row of droplets 22; and focus the collected EUV light at the central focusing position 220.

In one embodiment, the scanning direction 200 refers to the direction parallel to the ‘x’ axis. The rotation direction of the first reflective mirror 207 and the top focusing mirror 212 may be clock-wise under a top view.

The rotating speed of the first reflective mirror 207 may be a constant. The angular speed of the first reflective mirror 207 may be equal to the rotating angle of the first reflective mirror 207 when the first laser beam 31 bombards two adjacent droplets 22 in the first row of droplets 22 divided by the first time T1.

The rotating speed of the top focusing mirror 212 may be a constant. The angular speed of the top focusing mirror 212 may be equal to the rotating angle of the top focusing mirror 212 when the top focusing mirror 212 collects the EUV light generated by bombarding two adjacent droplets 22 divided by the first time T1.

When the first laser beam 31 is bombarding the first droplet of the first row of droplets 22, the second optical shutter 211 may block the second laser beam 32 from irradiating the irradiating position 202.

Further, as shown in FIG. 6 and FIG. 8, after the first laser beam 31 bombards all the droplets in the first row of droplets 22, the first reflective mirror 207 may arrive at a final position. The first resetting stage of the first sub-second signal 305 may cause the third sub driving device 205 to drive the first reflective mirror 207 to rotate back to the first initial position; and to be ready for bombarding the third row of droplets 22. At the same time, the first resetting stage of the first sub-third signal 316 may cause the plurality of the first sub-driving device 216 a to drive the top focusing mirror 212 to rotate back to the third initial position; and to be ready to collect the EUV light generated by bombarding the third row of droplets 22.

During the process for the top focusing mirror 212 to rotate back to the third initial position, the top focusing mirror 212 may still collect and focus the EUV light. Thus, to ensure the energy stability of the EUV light source, the top focusing mirror 212 and the bottom focusing mirror 213 may be staggered during the top focusing mirror 212 is rotated back to the third initial position. That is, when the top focusing mirror 212 and the bottom focusing mirror 213 meet at a certain angle, they may all focus on the gap between adjacent droplets 22; and may not focus on a same droplet at a same time. If the top focusing mirror 212 and the bottom focusing mirror 213 focus on a same droplet simultaneously, the EUV light focused at the central focusing point 220 may be significantly strong; and the intensity of the EUV light may have a spike; and the energy stability and uniformity may be affected. The staggered condition between the top focusing mirror 212 and the bottom focusing mirror 213 may be realized by adjusting the top focusing mirror 212 to rotate back slightly ahead, or slightly behind the schedule.

Further, after the last drop of the first row of droplets 22 is bombarded; and when the first drop of the second row of droplets 22 arrives at the irradiating position 202, the fourth sub-driving device 206 may drive the second reflective mirror 208 to accelerate from the first initial position to the second initial position. The second laser beam 32 may bombard the first droplet of the second row of droplets 22 arriving at the irradiating position 202. At the same time, the plurality of second sub-driving device 217 a may drive the bottom focusing mirror 213 to be at the first initial position; and may collect the EUV light generated by bombarding the first droplet of the second row of droplets 22.

Then, the first scanning stage of the second sub-second signal 306 may cause the fourth sub-driving device 206 to drive the second reflective mirror 208 to rotate with a constant speed starting from the second initial position; and the second laser beam 32 may scan along the scanning direction 200 to bombard other droplets of the second row of droplets 22 sequentially arriving at the irradiating positing 202.

At the same time, the first scanning stage of the second sub-third signal 317 may cause the second sub-driving device 217 a to drive the bottom focusing mirror 213 to rotate with a constant speed starting from the third initial position. During the rotation, the bottom focusing mirror 213 may sequentially collect the EUV light generated by bombarding the other droplets of the second row of droplets 22; and focus the collected EUV light at the central focusing point 220.

After the second laser beam 32 bombards all the droplets of the second row of droplets 22, the second reflective mirror 208 may arrive at a final position. The first resetting stage of the second sub-second signal 206 may cause the fourth sub-driving device 206 to drive the second reflective mirror 208 to rotate back to the first initial position; and to be ready for bombarding the fourth row of droplets 22 arriving at the irradiating position 202. At the same time, the first resetting stage of the second sub-third signal 317 may cause the plurality of second sub-driving device 217 a to drive the bottom focusing mirror 213 to rotate back to the third initial position; and to be ready to collect the EUV light generated by bombarding the fourth row of droplets 22.

During the process for the bottom focusing mirror 213 being rotated back to the third initial position, the bottom focusing mirror 213 may still collect EUV light, and focus the EUV light. Thus, to ensure a the stability of the EUV light at the focusing point 202, the bottom focusing mirror 213 and the top focusing mirror 212 may be staggered when the bottom focusing mirror 213 is rotated back to the third initial position. That is, when the top focusing mirror 212 and the bottom focusing mirror 213 meet at a certain angle, they should all focus on the gaps between adjacent droplets 22; and should not focus on a same droplet at a same time. If the top focusing mirror 212 and the bottom focusing mirror 213 focus on a same droplet at a same time, the EUV light irradiating from such a droplet may be significantly strong; and the EUV light focused at the central focusing point 220 may be have an energy spike. Such an energy spike may affect the energy stability and uniformity of the output EUV light. The staggered condition between the top focusing mirror 212 and the bottom focusing mirror 213 may be realized by adjusting the bottom focusing mirror 213 to rotate back slightly ahead, or slightly behind the schedule.

Such steps may be repeated until the last droplet of the plurality of droplets 22 is bombarded. Thus, the intensity of the EUV light at the central focusing point 220 may be increased. The EUV light focused at the central focusing point 220 may be the output EUV light of the EUV light source.

In one embodiment, detection units, such as position sensors, or counters, etc., may be used to detect if the first reflective mirror 207, the second reflective mirror 208, the top focusing mirror 212 and the bottom focusing mirror 213 have arrived the initial positions and final positions. The detected signals from the detection units may be feedback to the corresponding driving device to adjust the drive process of the first reflective mirror 207, the second reflective mirror 208, the top focusing mirror 212 and the bottom focusing mirror 213.

Thus, an exposure apparatus is provided according to the disclosed embodiments. The exposure apparatus may comprise the disclosed EUV light source; and other aspects of the present disclosure. The EUV light source may be used as a light source when the exposure apparatus is used to perform a photolithography process. FIG. 9 illustrates a block diagram of an exemplary exposure apparatus according to the disclosed embodiments.

As shown in FIG. 9, the exposure apparatus may include a base 91. The base 91 may be used to support other components of the exposure apparatus. The exposure apparatus also includes an EUV light source 92. The EUV light source 92 may be the disclosed EUV light source; and may be configured as an exposure light source for a photolithography process. Further, the exposure apparatus may also include a wafer stage 93. The wafer stage 93 may be configured to hold a wafer for forming patterns by the photolithography process. Further, the exposure apparatus may also include a reticle stage 94. The reticle stage 94 may be configured to hold a reticle (not shown) for the photolithography process. Further, the exposure apparatus may also include a control unit 95. The control unit 95 may be configured to control the exposure apparatus to perform the photolithography process.

Further, a method for generating EUV light is also provided according to the disclosed embodiments. FIG. 10 illustrates a corresponding flow chart for generating EUV light using the disclosed exposure apparatus. As shown in FIG. 10, the method may include spraying a plurality of droplets downwardly to an irradiating position through a spray nozzle array having a plurality of spray nozzles (S101); performing a scanning using a laser source to sequentially bombard the droplets arriving at the irradiating position to generate EUV light from each of the plurality of droplets (S102); and collecting and focusing the EUV light at a central focusing point using a reflective mirror having at least two first sub-focusing mirror and at least two second sub-focusing mirror (S103).

According to the disclosed embodiments, the disclosed EUV light source may include a spray nozzle array; and the spray nozzle array may include a plurality of spray nozzles. The plurality of spray nozzles may sequentially spray a plurality of rows of droplets downwardly to an irradiating position. Thus, the number of droplets supplied per unit time may be increased. Further, because each row of droplets aligned along a scanning direction may be sprayed out by different spray nozzles, the adjacent droplets to have a desired distance. Further, because the laser beam may scan along the scanning direction to sequentially bombard the plurality of droplets arriving at the irradiating position to generate EUV light, all the droplets arriving at the irradiating position may be bombarded by the laser beam; and the quantity of the generated EUV light may be increased. At the same time, the focusing mirrors may perform rotating scanning to simultaneously collect the EUV light generated by bombarding different droplets, and focus the collected EUV light at the central focusing point. The output power of the EUV light at the central focusing point may be increased.

Further, the focusing mirror of the disclosed EUV light source may include a top focusing mirror and a bottom focusing mirror. The top focusing mirror and the bottom focusing mirror may be separated; and the top focusing mirror may be disposed above the bottom focusing mirror. The top focusing mirror may include at least two separated first sub-focusing mirrors; and the bottom focusing mirror may include at least two separated second sub-focusing mirrors.

Further, the first driving device of the disclosed EUV light source may include at least two first sub-driving devices and at least two second sub-driving devices. Each of the first sub-driving devices may be connected with a first sub-focusing mirror; and each of the second sub-driving devices may be connected with a second sub-focusing mirror. Thus, the area and mass of the first sub-focusing mirror driven by the first sub-driving device and the second sub-focusing mirror driven by the second sub-driving device may be relatively small.

Therefore, the driving force may be rapidly transferred to each position of the first sub-focusing mirror and the second sub-focusing mirror. The starting time or rotations of the first sub-focusing mirrors and the second sub-focusing mirrors may be identical; and it may not cause the rotation of the first sub-focusing mirror and the second sub-focusing mirror to lag behind at a certain position. Thus, the EUV light collected by the top focusing mirror and the bottom focusing mirror during the rotating scanning may all be focused at the central focusing position. Therefore, the power of the EUV light at the central focusing point may be increased.

Further, the reflective mirror of the disclosed EUV light source may include a first reflective mirror and a second reflective mirror. The second driving device of the disclosed EUV light source may include a third sub-driving device and a fourth sub-driving device. The first reflective mirror may be disposed above the second reflective mirror. The first reflective mirror may reflect a portion of the laser beam to form a first laser beam. The third sub-driving device may be connected with the first reflective mirror to drive the first reflective mirror to rotate. When the first reflective mirror is rotating, the first laser beam may scan along a scanning direction. The second reflective mirror may reflect a portion of the laser beam to form a second laser beam. The fourth sub-driving device may be connected with the second reflective mirror to drive the second reflective mirror to rotate. When the second reflective mirror is rotating, the second laser beam may scan along a scanning direction.

Further, the first driving device of the disclosed EUV light source may include a first sub-driving device and a second sub-driving device. The first sub-driving device may be connected with the top focusing mirror; and may be configured to drive the top focusing mirror to perform a rotate scanning. The second sub-driving device may be connected with the bottom focusing mirror; and may be configured to drive the bottom focusing mirror toe perform rotate scanning. Thus, the first laser beam and the second laser beam of the disclosed EUV light source may be able to alternately bombard adjacent rows of droplets. Correspondingly, the top focusing mirror may collect the EUV light irradiating from the droplets generated by bombarding the droplets using the first laser beam, and focus the collected EUV light at the central focusing position. The bottom focusing mirror may collect the EUV light irradiating from the droplets generated by bombarding the droplets using the second laser beam; and focus the collected EUV light at the central focusing position. Thus, the output power of the EUV light at the central focusing position may be further increased.

The above detailed descriptions only illustrate certain exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention. Those skilled in the art can understand the specification as whole and technical features in the various embodiments can be combined into other embodiments understandable to those persons of ordinary skill in the art. Any equivalent or modification thereof, without departing from the spirit and principle of the present invention, falls within the true scope of the present invention. 

What is claimed is:
 1. An extreme ultraviolet (EUV) light source, comprising: a spray nozzle array having a plurality of spray nozzles configured to spray a plurality of rows of droplets to an irradiating position; a laser source configured to generate a first laser beam and a second laser beam and cause the first laser beam and the second laser beam to alternately bombard the rows of droplets to generate EUV light; a focusing mirror having at least two first sub-focusing mirrors and at least two second sub-focusing mirrors; a first driving device having at least two first sub-driving devices and at least two second sub-driving device, each of first driving devices driving one of the first sub-focusing mirrors and each of the second sub-driving devices driving one of the second sub-focusing mirrors; and a control unit configured to synchronously control the spray nozzle array, the laser source and the focusing mirror.
 2. The EUV light source according to claim 1, wherein: the first laser beam and the second laser beam alternately bombard different rows of droplets to generate the EUV light.
 3. The EUV light source according to claim 1, further including: a laser, a reflective mirror and a second driving device, wherein: the reflective mirror includes a first reflective mirror and a second reflective mirror, and the first reflective mirror is disposed above the second reflective mirror; the first reflective mirror is configured to generate the first laser beam from the laser; and the second reflective mirror is configured to generate the second laser beam from the laser.
 4. The EUV light source according to claim 3, wherein: the second driving device includes a third sub-driving device and a fourth sub-driving device; the third sub-driving device is connected to the first reflective mirror to drive the first reflective mirror to scan along a scanning direction; and the fourth sub-driving device is connected to the second reflective mirror to drive the second reflective mirror to scan along the scanning direction.
 5. The EUV light source according to claim 3, wherein the control unit configured to output synchronized first signals, second signals, and third signals, wherein: the first signals are configured to control the plurality of spray nozzles to sequentially spray the rows of droplets; the second signals are configured to control the second driving device to drive the first and second reflective mirrors to synchronically rotate; and the third signals are configured to control the first driving device to drive the focusing mirror synchronically rotate.
 6. The EUV light source according to claim 5, further including: a first optical shutter disposed between the first reflective mirror and the irradiating position, and configured to selectively block the first laser beam from irradiating the irradiating position; and a second optical shutter disposed between the second reflective mirror and the irradiating position, being configured to selectively block the second laser beam from irradiating the irradiating position.
 7. The EUV light source according to claim 6, wherein: the first optical shutter includes a first blocking unit and a third driving device connected with the first blocking unit; the second optical shutter includes a second blocking unit and a fourth driving device connected with the second blocking unit; the third driving device is configured to drive the first blocking unit to be on or away from the optical path of the first laser beam irradiating the irritating position; and the fourth driving device is configured to drive the second blocking unit to be on or away from the optical path of the second laser beam irradiating the irradiating position.
 8. The EUV light source according to claim 7, wherein: the first blocking unit is a third reflective mirror reflecting the first laser beam to a direction other than the optical path of the first laser beam irradiating the irradiating position when the first blocking unit is blocking the first laser beam; and the second blocking unit is a fourth reflective mirror reflecting the second laser beam to a direction other than the optical path of the second laser irradiating the irradiating position when the second blocking unit is blocking the second laser beam.
 9. The EUV light source according to claim 8, further including: a heat recycling unit configured to absorb the first laser beam reflected by the first reflective mirror and the second laser beam reflected by the second reflective mirror.
 10. The EUV light source according to claim 1, wherein: the light focusing mirror includes a top focusing mirror and a bottom focusing mirror disposed below the top focusing mirror.
 11. The EUV light source according to claim 1, wherein: distances between centers of adjacent spray nozzles are identical.
 12. The EUV light source according to claim 11, wherein: a size of the droplets is in a range of approximately 25 μm˜35 μm; and a distance between the centers of adjacent spray nozzles is in a range of approximately 45 μm˜75 μm.
 13. The EUV light source according to claim 1, wherein: the droplets are made of one of Sn, Sn alloy, Sn compound, Xe and Li.
 14. The EUV light source according to claim 1, wherein: the plurality of spray nozzles are distributed along a scanning direction.
 15. A method for generating EUV light, comprising: spraying a plurality of droplets downwardly to an irradiating position through a spray nozzle array having a plurality of spray nozzles; performing a scanning using a laser source to sequentially bombard the droplets arriving at the irradiating position to generate EUV light from each of the plurality of droplets; and collecting and focusing the EUV light at a central focusing point by a focusing mirror having at least two first sub-focusing mirrors and at least two second sub-focusing mirrors; and a first driving device having at least two first sub-driving devices and at least second sub-driving device, wherein spraying the plurality of droplets, performing the scanning and collecting and focusing the EUV light are synchronously controlled by a control unit.
 16. The method according to claim 15, wherein spraying the plurality of droplets downwardly to an irradiating position further includes: sequentially spraying a first droplet from each of the plurality of spray nozzles with time interval of a first time.
 17. The method according to claim 16, wherein: the first droplet sequentially sprayed from each of the plurality of spray nozzles form a first row of droplets; and a first laser beam and a second laser beam of the light source sequentially bombard each of the first droplet in the first row of droplets.
 18. The method according to claim 17, further including: sequentially spraying a second droplet from each of the plurality of spray nozzles with each second droplet lagging behind the corresponding first droplet with a time interval of a second time.
 19. An exposure apparatus, comprising: a base, an EUV light source configured as an exposure light source for a photolithography process; a wafer stage configured to hold a wafer for forming patterns by the photolithography process; a reticle stage for holing a reticle for the photolithography process; and a control unit configured to control the exposure apparatus to perform the photolithography process, wherein the EUV light source comprises a spray nozzle array having a plurality of spray nozzles configured to spray a plurality of rows of droplets to an irradiating position; a laser source configured to generate a first laser beam and a second laser beam and cause the first laser beam and the second laser beam to alternately bombard the rows of droplets to generate EUV light; a focusing mirror having at least two first sub-focusing mirrors and at least two second sub-focusing mirrors; and a first driving device having at least two first sub-driving device and at least two second sub-driving device, each of first driving devices driving one of the first sub-focusing mirrors and each of the second sub-driving devices driving one of the second sub-focusing mirrors, the spray nozzle array, the laser source and the focusing mirror are synchronously controlled by a control unit.
 20. The exposure apparatus according to claim 19, wherein: each of the first sub-driving devices drives one of the first sub-focusing mirrors; and each of the second sub-driving drives one of the two second sub-focusing mirrors. 